BACKGROUND: Prostatic cancer is one of the most common cancers of males in a Sudanese population. The early detection is very important, as it is only curable at an early stage. AIM: The objective of this study was to investigate the expression pattern of Ki-67 in benign and malignant prostatic lesions to improve the diagnosis that may help in better management and prevention of disease. MATERIAL AND METHODS: Fifty-eight formalin fixed paraffin blocks from diagnosed cases of prostatic tumours with different grade, and stages were included in this study. Ki-67 expression was examined immunohistochemically by using monoclonal mouse anti-human Ki67 IS626. The results were correlated with Gleason score and tumour differentiation and stage. RESULTS: The frequency of histological types was as follow: 11 cases of benign prostate,atic hyperplasia (19%) and 47 cases of prostatic cancer (81%). Our results stated that prostatic adenocarcinoma among Sudanese patients was of low grade which means tumours are less aggressive. Furthermore, the findings demonstrate that Ki-67 expression in prostatic carcinoma smears was correlated significantly with the degree of Gleason score (P < 0.05). CONCLUSIONS: We found that the prostatic adenocarcinoma among Sudanese patients was less aggressive. Furthermore, Ki-67 expression was proportional to the grade of a tumour and it was a useful prognostic and diagnostic biomarker. © 2018 Albasheer Abdelmalik Mohamed, Mohammed Yousif Abbas, Hajed Alharbi, Ali Yousif Babiker.